Approximately 10% of patients acutely infected with hepatitis B virus (HBV) continue to carry the virus resulting in the existence of more than 200 million chronic HBV carriers worldwide. Some of these individuals will develop cirrhosis and a smaller subset will progress to hepatocellular carcinoma (HCC). Although HBV has not been established as a causative agent of HCC, there are experimental results that strongly suggest it may have a role. Several HBV gene products are expressed in the liver tumor cell and adjacent nontumorous liver tissue of patients with primary HCC; these include the HBsAg and HBxAg. In light of this information, it is surprising that essentially nothing is known about the effect of HBV infection and subsequent gene expression on cellular gene expression by liver cells. The investigators have previously established a series of well differentiated SV40 immortalized rat hepatocyte cell lines that express albumin and other liver specific genes at liver like levels and have used these cell lines to study ras transformation and the molecular mechanisms of albumin expression. They have also developed a long-term primary hepatocyte culture system using dimethylsulfoxide that can be used to study immortalization and transformation of hepatocytes by viral and cellular oncogenes. In preliminary studies, they have transfected an SV40-immortalized cell line, CWSV1, with expression vectors containing genes for HBsAg and generated a series of cell lines that express HBsAg. Initial characterizations show that the cell lines which produce high levels of HBV surface antigen transcripts and polypeptides express reduced levels of alpha-1 antitrypsin, transferrin and albumin RNAs. Transfection of CWSV1 cells with a head to tail tetramer of HBV DNA yielded cells that produced HBsAg and HBxAg suggesting that HBV may be capable of replicating in CWSV1 cells and producing infectious virus. The goals of the proposed study are to use these two in vitro hepatocyte systems to thoroughly and systematically determine the effects of HBV infection and/or expression of specific HBV gene products, on expression.